A bright mayonnaise dressing with lemon and Old Bay seasoning marries the flavors of shrimp, celery and scallions. Serve this easy shrimp salad over Bibb lettuce or a spring mix.
Pour water into a large Dutch oven. Halve 1 lemon; squeeze juice from both halves into the water, then add the lemon halves to the pot. Bring to a boil over high heat. Add shrimp; cook, stirring occasionally, just until the shrimp turn pink, 2 to 3 minutes. Drain. Spread the shrimp in an even layer on a large rimmed baking sheet. Let cool for 20 minutes. Peel, devein and coarsely chop the shrimp.
Squeeze 2 tablespoons juice from the remaining lemon into a large bowl. (Reserve the remaining juiced lemon for another use.) Add celery, scallions, mayonnaise, mustard, Old Bay and cayenne; stir to combine. Stir in shrimp. Cover and refrigerate until the salad is cold and the flavors have melded, at least 2 hours (and up to 3 days). Garnish with dill just before serving, if desired.